Single-Electron Tunnel Junction for a Complementary Metal-Oxide Device and Method of Manufacturing the Same

ABSTRACT

A method of providing a p-type substrate, disposing a pad oxide layer on the p-type substrate, disposing a nitride layer on the pad oxide layer, forming a nitride window in the nitride layer, disposing a field oxide in the nitride window, disposing a polysilicon gate over the field oxide, and diffusing a n-doped region in the p-type substrate, thereby forming at least one single-electron tunnel junction between the polysilicon gate and the n-doped region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of U.S. Provisional Application Ser. No. 60/823,787 filed on Aug. 29, 2006, entitled “Self-Synchronization of Oscillators with Single-Electron Restoration,” commonly assigned with this application and incorporated herein by reference in its entirety, and is related to application Ser. No. ______, Docket No. TI-63240, entitled “Single-Electron Injection/Extraction Device for a Resonant Tank Circuit and Method of Operation Thereof” and is also related to application Ser. No. ______, Docket No. TI-65284, entitled “A Parallel Redundant Single-Electron Device and Method of Manufacture”, both to be filed concurrently herewith.

TECHNICAL FIELD

The disclosure is directed, in general, to single-electron tunnel junction, and more specifically, to a single-electron tunnel junction and its method of manufacture in an integrated circuit using complementary metal-oxide semiconductor (“CMOS”) process.

BACKGROUND

A component of a single-electron circuit is a single-electron tunnel junction. Generally, a single-electron tunnel junction has a structure similar to a parallel-plate capacitor. In the present Application, the term “single-electron device” is also commonly used to describe the single-electron tunnel junction. In the single-electron tunnel junction, two plates are separated by a dielectric. However, the single-electron tunnel junction has two special properties.

Regarding the first property, the dielectric has to be thin enough to allow for quantum-mechanical tunneling of electrons through the dielectric to occur with an applied electric potential (e.g. around 1 Volt). Regarding the second property, the capacitance of the structure should be small, so small in fact that the addition of a single electron into the single-electron tunnel junction would result in a significant voltage change, such as 0.5 volts.

An aspect of the disclosure provides a method of manufacturing a single-electron tunnel junction device. The method includes: providing a p-type substrate, disposing a pad oxide layer on the p-type substrate, disposing a nitride layer on the pad oxide layer, forming a nitride window in the nitride layer, disposing a field oxide in the nitride window, disposing a polysilicon gate over the field oxide and diffusing a n-doped region in the p-type substrate, thereby forming at least one single-electron tunnel junction between the polysilicon gate and the n-doped region.

Another aspect of the disclosure includes a single-electron tunnel junction device. The single-electron tunnel junction device includes a p-type substrate, an n-doped region disposed in the p-type substrate, a pad oxide disposed over the n-doped region, a field oxide to a side of the n-doped region, and a polysilicon gate disposed over the field oxide and the pad oxide.

Another aspect of the disclosure includes a parallel array single-electron tunnel-junction device. The parallel array single-electron tunnel junction device includes the above-described single-electron tunnel-junction device. The parallel array single-electron tunnel-junction device further includes a second single-electron tunnel-junction including: the p-type substrate, a second n-doped region disposed on the p-type substrate, a second pad oxide disposed over the second n-doped region, a second polysilicon gate disposed over the second field oxide and said second pad oxide, wherein at least two of the parallel redundant single-electron tunnel devices have a differing capacitance as a function of a difference between: a) a first distance measured between the first n-doped region and the first polysilicon gate, and b) a second distance measured between the second n-doped region and the second polysilicon gate.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure is described with reference to example embodiments and to accompanying drawings, wherein:

FIG. 1A illustrates a top view of one embodiment of a single-electron device constructed according to the principles of the disclosure;

FIG. 1B illustrates a cross-sectional view of one embodiment of a single-electron device constructed according to the principles of the disclosure;

FIG. 2A illustrates a top view of one embodiment of a dual single-electron device constructed according to the principles of the disclosure;

FIG. 2B illustrates a plurality of dual single-electron devices constructed according to the principles of the present disclosure;

FIG. 3A illustrates a redundant array of single electron tunnel-junction devices constructed according to the principles of the present disclosure;

FIGS. 3B and 3C illustrate misalignments of an active mask and a polysilicon mask of FIG. 3A when generating redundant arrays of single-electron devices;

FIG. 4 illustrates a multiplexer circuit for accessing a plurality of single-electron tunnel junction devices constructed according to the principles of the present disclosure;

FIG. 5A illustrates a flow chart of one embodiment of a method of manufacturing a single-electron tunnel junction in a CMOS carried out according to the principles of the disclosure;

FIG. 5B illustrates a flow chart of one embodiment of a method of manufacturing a redundant array of single-electron tunnel junctions in a CMOS carried out according to the principles of the disclosure;

FIGS. 6A-6G illustrate cross-section views of selected steps in example implementation of a method of fabricating an single-electron tunnel junction in a CMOS constructed according to the principles of the disclosure; and

FIG. 7 illustrates simplified block diagram illustrating an example mobile communication device incorporating the single-electron device frequency oscillation and/or generation mechanism of the disclosure.

DETAILED DESCRIPTION

FIG. 1A illustrates a top view of one embodiment of a single-electron device 100 constructed according to the principles of the disclosure. A single-electron tunnel junction 145 created from a layer of an n-doped region 120, an interposing pad oxide (not illustrated) and a polysilicon gate 140. In FIG. 1A, the dashed-line around the n-doped area 120 and the polysilicon gate 140 indicates a desired or drawn geometry, while the solid area 120 and 140 indicates the fabricated geometry—after taking into account limitations and imperfections in the manufacturing process such as lithographic error and over-etching. In this disclosure, “pad oxide” is defined as a dielectric that performs an isolation function but with some measurable capacitance, whereas a “field oxide” is defined as a dielectric that substantially provides only an isolation function. In one embodiment, the n-doped region 120 is doped with arsenic or phosphorous, and the polysilicon gate is doped with boron.

An overlap area between the n-doped region 120 and the polysilicon gate 140, which form two plates of a capacitor-like structure, should be small, on the order of 5-10 nanometers (nm) by 5-10 nm so that the capacitance is below, in this example, 1 attoFarad (“aF”). However, such a design constraint creates problems when trying to manufacture single-electron tunnel junctions using standard CMOS fabrication techniques. Generally, ensuring that a sufficiently small capacitance is realized in a single-electron tunnel device can be a difficult challenge when fabricating the single-electron tunnel junction.

For instance, if too large of a capacitance is created, then the voltage change resulting from the addition of a single-electron to the structure might not be differentiable from voltage fluctuation due to thermal noise. One alternative to reduce the capacitance of a parallel plate structure is to arbitrarily increase the thickness of the dielectric layer. However, this is disallowed in the fabrication a single-electron tunnel junction, as it would inhibit the occurrence of quantum mechanical tunneling of electrons, which is desired in the single-electron tunnel junction. Although a small structure with a small capacitance is desired, reliable fabrication of such structures stretches the limits of today's MOS and CMOS fabrication processes.

Generally, by making the single tunnel junction 145 sufficiently small, and with an insertion of a suitable pad oxide (to be discussed below) inserted between n-doped region 120 and polysilicon gate 140, a capacitor is formed. By making this area of overlap suitably small, a capacitance is formed whose size is on the same order of magnitude to a charge of a single electron.

FIG. 1B illustrates one embodiment of cross-sectional view of a single-electron device 100 constructed according to the principles of the disclosure. A substrate 155 has disposed thereon the n-doped region 120. This cross-sectional view is taken on line 160 on FIG. 1A. In one embodiment, the substrate 155 is a p-type substrate.

The substrate 155 also has a field oxide 122 disposed on and to a side of the substrate 155. A pad oxide 123 covers the n-doped region 120 with a thin oxide layer.

The gate polysilicon 140 overlies both the field oxide 122 and an overhang of the n-doped region 120 with the thin layer of pad oxide 123 interposed between. This creates the single-electron tunnel junction 145. In other words, the polysilicon gate 140, disposed over part of the thin layer of pad oxide 123, which is disposed over the n-doped region 120, forms a capacitance. In some embodiments, a bracing area 180 is used to help support the structure of the polysilicon gate 140. In one embodiment, the single-electron tunnel junction 145 has about a 5 nm by 5 nm area, giving rise to a capacitance of 0.3 attofarads. As a charge of an electron is approximately 1.6×10⁻¹⁹ coulombs, an addition of a single electron would result in a voltage change of approximately 0.5 volts. For ease of explanation, any stray capacitance of the polysilicon gate 140 is assumed negligible. That is an example of acceptable single-electron tunnel-junction or, which has good characteristics for measuring and exploiting single-electron effects. In other embodiments, 0.1 volts may be set as a threshold. Single electron devices below this discernable threshold may be deemed unacceptable for single-electron effects. However, these voltage changes may be generally measurable above variations in background thermal noise.

In some embodiments, the thickness of the n-doped region 120 is about 90 nm. The thickness of the pad oxide 123 is about 1.2 nm. In some embodiments, the capacitance of the single-electron tunnel junction 145 is sufficiently small such that the addition of a single electron to the structure would result in a voltage change that is substantially equal to 1 Volt.

FIG. 2 illustrates one embodiment of top view of a dual single-electron device 200 constructed according to the principles of the disclosure. In the device 200, n-doped regions 220, 230 are both disposed under a polysilicon gate 240, with a thin layer of pad oxide (not illustrated) disposed in between.

In some embodiments, the polysilicon gate 240 is disposed over a part of a pad oxide, which is in turn disposed over the n-doped region 230. The capacitance of the n-doped region 230 compensates for a deficiency of a capacitance formed by the polysilicon gate 240 disposed over a part of the pad oxide disposed, in turn, over the n-doped region 220. In other words, if the polysilicon gate 240 is misaligned with respect with its placement over the n-doped region 220 such that the capacitance of the resulting single-electron tunnel junction 245 is too large or too small, a second single-electron tunnel junction 247 compensates for it. By regarding the single-electron tunnel junctions 245, 247 together as a unit having an aggregate capacitance equivalent to the capacitance of two single-electron tunnel junctions, the relative placement of the polysilicon gate 240 to the n-doped region 220 are varied in offset, as will be described below. In FIG. 2, the n-doped regions 220, 230 are coupled through metal contacts 250, 255 through a metal connection 257.

Generally, because a desired overlap between an n-doped region and a polysilicon gate is small, precise alignment between the n-doped region and the polysilicon gate is important. This means the alignment between a mask for placement of the n-doped region (“active” mask) and a polysilicon mask should be precise. If the active mask and the polysilicon masks are not precisely aligned, then excess capacitance might result, or no overlap region would result. For instance, for a desired 5 nm by 5 nm overlap, a standard deviation for mask alignment error of 5 nm in a 45 nm gate-length CMOS process generation, results in no gate overlap whatsoever.

Generally, the dual single-electron tunnel device 200 can help alleviate this problem. Using the dual single-electron device of FIG. 2, if a small alignment offset exists between the polysilicon gate 240 and the n-doped region 220, the aggregate capacitance of both of the single-electron tunnel junctions 245, 247 is substantially constant.

Based on the dual single-electron tunnel device 200, the smallest single-electron tunnel junction that can be fabricated, with a relatively high yield, can be estimated. In one embodiment, a fabrication tool has a worst-case alignment offset of r radially between the n-doped region 220 and a mask for the polysilicon gate 240. Therefore, through use of the dual single-electron device 200, aggregate capacitance can be made substantially constant for offsets that are not too “large,” such as an offset of 5 nm.

For instance, FIG. 2B illustrates various offsets between the n-doped region 220, 230 and the polysilicon gate 240. As is illustrated between the first two figures, a deficiency in overlap between the n-doped region 220 and the polysilicon gate 240 is compensated for by the n-doped region 230.

FIG. 3A generally illustrates one embodiment of a deliberate changing of offsets for various single electron tunnel junction devices to generate a parallel redundant array of single-electron tunnel devices having single-electron tunnel junctions 310, 320, 330, 340 constructed according to the principles of the disclosure. Generally, in the array 300, a plurality of n-doped regions 312, 322, 332, and 342 are placed at different offsets 315, 325, 335, 345 in respect to their respective polysilicon gates 314, 324, 334, 344.

Generally, lithography and etching processes to manufacture MOS devices, such as single-electron tunnel junctions, are not completely error-free in the sense that a desired geometry would not appear exactly the same on a fabricated silicon. This is especially true wherein the minimum feature sizes of the MOS and CMOS devices are already much smaller than the ultra-violet light wavelength used to define them in the lithography process. This creates limitations on a CMOS fabrication system.

One prevalent effect associated with this limitation is that square edges are rounded. Mask offset is also a problem, along with other variations in fabrication process. These other variations could be due to a non-uniform density of an etching solution or due to other imperfections in a lithography process in a standard CMOS process. Employment of the parallel redundant array 300 could be employed in a plurality of situations in order to improve an overall yield.

Employment of the parallel redundant array 300 could help, first, because a selected dimension of the single-electron tunnel junction might be much smaller than a worst-case alignment margin afforded by a fabrication tool. In this case, the dual-single-electron device 200 may not be sufficient to ensure that a sufficiently small overlap area is produced. Secondly, a random variation in the fabrication process might alter the geometry of the polysilicon gate and the n-doped region in a way not predicted, which again would change the effective overlap area, which would change the capacitance.

In these cases, or in other cases, a parallel redundant structure, such as the parallel redundant array 300, can be used. In the parallel redundant array 300, as discussed above, several tunnel junction structures are drawn in parallel with different overlap (or gap) drawn between the n-doped region and the polysilicon gate. This redundancy is performed in numbers to help guarantee that regardless of the mask-shifts, rounding effects, or other random variations, at least one of the structures results in a selected amount of capacitance. Because the individual size of the tunnel junction is small, manufacturing a redundant array of these devices should not take a significant amount of area. The redundant array device 300 can provide a high resulting yield for the overall system, even if fabrication of individual single-electron tunnel junctions might prove to be unreliable.

Generating the redundant array 300 in such a manner can help ensure that an acceptable single-electron tunnel junction is created somewhere in the redundant array 300. By deliberately varying the offset between the n-doped region and the polysilicon gate in the device layout, misalignment of masks of the polysilicon during the fabrication process can be rendered less critical, as one of the single-electron devices 310, 320, 330, 340 would have an overlap that is closest to a desired overlap.

As is illustrated, the different offsets 315, 325, 335, 345 have differing areas of overlap or distance between their respective n-doped regions and polysilicon gates, different capacitances are created. Through one-time factory or even power-up testing, it can be determined which of the single-electron tunnel junctions 310, 320, 330, 340 best meets capacitance specifications.

FIG. 3B shows the active mask 391 and the polysilicon mask 392 used to fabricate the plurality of single-electron devices 300. The exposed area 316, 326, 336, 346 in the active mask 391 defines the resulting printed geometry of the n-doped region 312, 322, 332, and 342 respectively. Similarly the exposed area 318, 328, 338, 348 in the polysilicon mask 392 is used to print the polysilicon structure 314, 324, 334, and 344 respectively. If the two masks 391 and 392 are aligned correctly, then the plurality of devices shown in FIG. 3A would result. Note that the geometry shown in FIG. 3A also includes other fabrication errors such as over-etching, lithography errors etc. In this case the single-electron tunnel-junction 320 has the right amount of capacitance, with the rest having either too much or too little to no overlap area.

FIG. 3C shows a resulting printed geometry of a polysilicon mask that is misaligned by a direction and amount indicated by arrow 380 in relation to the placement of the active mask. As seen in FIG. 3C, the single-electron tunnel junction 330 instead of 320 has the right amount of overlap area to evince an acceptable single-electron effect.

Although fabrication techniques, through differing offsets, may lead to manufacturing yields wherein the number of single-electron devices that have acceptable single-electron effects may be relatively low for a given manufacturing run, e.g., 20.0%, the present disclosure recognizes that, through adapting CMOS manufacturing techniques, there is an efficiency in producing a high number of single-electron devices, and then selecting a subset of those high number single-electron devices that evince an acceptable single-electron effect (e.g., voltage change due to a single-electron that is discernable from thermal noise). Due to the relatively small chip area or “real estate” that the single-electron devices occupy, manufactures may generate, through varying offsets, a sufficient number of single-electron devices on a given chip.

FIG. 4 illustrates a circuit 400 for selecting from one single electron tunnel junction device from a plurality of the single-electron tunnel devices constructed according to the principles of the present disclosure. The single-electron tunnel devices 410, 420, 430 and 440 are coupled to a multiplexer 450. Each single-electron tunnel device 410 through 440 can be selected by a select line. Therefore, a functional single electron tunnel device can be selected. An output of a selected single-electron tunnel device is considered active when selected by the multiplexer 450. Note that the selection could be done by other means, such as selective of the input voltage to each of the single-electron devices. In that case the multiplexer 450 would not be a physical multiplexer as shown in FIG. 4, but a multiplexer mechanism, firmware or software with a variety of approaches to a specific realization of the physical selection. In some embodiments, each of the single electron devices has a different internal alignment offset, and is selectable by the multiplexer 450. The number of the single-electron devices to be selected could be very high, even up to a million or more.

As exemplarily illustrated in single electron device 410, each of the plurality of single-electron circuit 410, 420, 430, 440 include a tunneling junction, such as tunneling junction 410, in series with a capacitor 412. In some embodiment, the capacitor 412 is a “non-tunneling” capacitor; in other words, no appreciable tunneling effects occur between the anode and the cathode of this capacitor. This is only one example of many possible single-electron devices. The capacitor 412 can be fabricated by stacking a metal layer on top of the polysilicon gate 140. This type of structure, such as shown within single-electron device 410, is similar to a “Coulomb blockade”.

FIGS. 5A and 5B illustrates a flow chart of one embodiment of a method of manufacturing a single-electron tunnel junction in a method 500 carried out according to the principles of the disclosure. These will be described in relation to both the FIGS. 6A-6G, and will be cross-correlated with the FIG. 1B as appropriate. Generally, method 500 is a variation on CMOS fabrication techniques, and the method can advantageously be used in CMOS fabrication facilities.

In a step 510, a p-type substrate is provided. In one embodiment, this is a p-type substrate 510 of FIG. 5A. In one embodiment, after etching and other processing has occurred, the p-type substrate 510 correlates to the substrate 155 of FIG. 1B.

In a step 515, a pad oxide layer is disposed on the p-type substrate. In one embodiment, the pad oxide layer is a pad oxide 615 of FIG. 5B, which is disposed on the p-type substrate 610. In some embodiments, at least part of the pad oxide 715 is later to be employed as the pad oxide 123 of FIG. 1B.

In a step 520, a nitride layer is disposed on the pad oxide. In one embodiment, the nitride layer is a nitride layer 720 of FIG. 6B, which is disposed on the pad oxide 715.

In a step 525, a nitride window is formed in the nitride layer. In one embodiment, the nitride windows are nitride windows 830, 832 of FIG. 6C. In one embodiment, the nitride window 730 and 732 is created by using a combination of photolithography and etching, as may be used in a standard CMOS process. As is illustrated, the etching process only removes a part of the nitride layer, as defined by a photolithography mask. The etching process in the step 525 does not remove the pad oxide 715.

In a step 530, a field oxide is disposed in the nitride window. In one embodiment, the field oxide is a field oxide 945 of FIG. 5D. The pad oxide 715 and the field oxide 945 have the same chemical composition, which is silicon dioxide. Once a nitride window is formed, the chip “die”, containing the pad oxide 715 and the field oxide 945 is then heated, such as being placed in a furnace. Any area of the chip “die” that is not covered by the nitride layer 720 undergoes further oxidation. This oxidation process then ‘grows’ or expand the pad oxide layer 715 above and below the existing pad oxide 715. When undergoing the oxidation process, the nitride layer also gets very slowly oxidized, but occurs at a much slower rate than the oxidation process in exposed silicon/silicon dioxide of the chip. In some embodiments, the nitride layer 720 after this step is slightly “rounded.”

In a step 535, the nitride layer is removed. In one embodiment, the nitride layer 520 is illustrated as removed in a FIG. 5E.

In a step 540, a polysilicon gate is disposed over the field oxide. The polysilicon gate is defined through a photolithography process with a separate masking layer. In one embodiment, the polysilicon gate is a polysilicon gate 1050 of FIG. 6F. In one embodiment, the polysilicon gate 1050 correlates to the polysilicon gate 240 of FIG. 2A.

In a step 545, an n-doped region is implanted in the p-type substrate, thereby forming at least one single-electron tunnel junction between the polysilicon gate and the n-doped regions. The area for implantation is also defined through a photolithography process with a separate mask layer. In one embodiment, the n-doped regions are the n-doped regions 1160 and 1162 of FIG. 6G. This diffusion of n-doped regions creates single-electron tunnel junctions 1165, 1167 between the n-doped regions 1160, 1162, and the polysilicon gate 1050, respectively. In one embodiment, after method 500, the n-doped regions 1160, 1162 correspond to the n-doped region 220 and 230 of FIG. 2A.

In one embodiment, the field oxide is provided to a side of the p-type substrate. The n-doped region is diffused beneath the polysilicon gate to form a single tunnel junction. A first and second tunnel junction is formed at a first and second end, respectively, of the polysilicon gate.

In one embodiment of the method 500, a first mask is provided for use with diffusing the n-doped region in the p-type substrate. A second mask is provided for use with disposing the polysilicon gate. A first and second single-electron tunnel junction is employed to help alleviate a mask-alignment mismatch between the first mask and the second mask.

FIG. 5B illustrates a flow chart of one embodiment of a method 550 of manufacturing a redundant array of single-electron tunnel junctions in a MOS or CMOS practiced according to the principles of the disclosure.

In a step 560, a mask is provide for diffusing a plurality of n-doped regions defined by a first set of a plurality of exposed regions of a mask.

In a step 570, a mask is provided for disposing a plurality of n-doped active areas defined by a plurality of exposed areas is staggered in length. In other words, the lengths of the exposed areas of the mask are of differing lengths.

In a step 580, a parallel redundant array of single-electron devices are manufactured as a function of the offsetting, such as illustrated in the method of FIG. 5A.

FIG. 7 illustrates a simplified block diagram illustrating an example communication device 870 incorporating the single-electron device and single-electron oscillator constructed according to the principles of the present invention. The communication device may comprise any suitable wired or wireless device such as a multimedia player, mobile station, mobile device, cellular phone, PDA, wireless personal area network (WPAN) device, Bluetooth EDR device, etc. For illustration purposes only, the communication device is shown as a cellular phone or smart phone. Note that this example is not intended to limit the scope of the invention as the SED mechanism of the present invention can be implemented in a wide variety of wireless and wired communication devices.

The cellular phone, generally referenced 870, comprises a baseband processor or CPU 871 having analog and digital portions. The basic cellular link is provided by the RF transceiver 894 and related one or more antennas 896, 898. A plurality of antennas is used to provide antenna diversity which yields improved radio performance. The cell phone also comprises internal RAM and ROM memory 910, Flash memory 912 and external memory 914.

In accordance with one aspect of the present disclosure, a single electron device 928 is employed by the RF transceiver 894. The single electron device 928 could be either internal or external to the RF transceiver 894. In some embodiments, the radio frequency device includes a plurality of single electron devices in an array, such as described in FIG. 3A, or can be dual single electron devices, such as in FIG. 2A.

Generally, the single-electron devices could be used for generation of local oscillator clocks. The single electron device could also be used to generate a stable bias current reference or voltage reference for various analog and RF circuits that comprise the radio. The current can be accurately generated by exploiting the single-electron characteristic of a Coulomb blockade in which a single-electron (i.e., charge) transfer is virtually guaranteed beyond a certain time interval, which is typically on the order of tens of picoseconds. Moving a fixed charge “e” within a well-controlled period “T” of a clock in a repetitive manner will give rise to a well-controlled current I=e/T, which could be used in as a low-noise reference current for analog and RF circuits. To increase this current, multiple single electron devices could be used. An output of the plurality of the single-electron devices is controlled to be active or inactive, such as by the multiplexer 450 of FIG. 4.

Several user interface devices include microphone 884, speaker 882 and associated audio codec 880, a keypad for entering dialing digits 886, a vibrator 888 for alerting a user, camera and related circuitry 900, a TV tuner 902 and associated antenna 104, display 106 and associated display controller 908 and GPS receiver 890 and associated antenna 892.

A USB interface connection 878 provides a serial link to a user's PC or other device. An FM receiver 872 and antenna 874 provide the user the ability to listen to FM broadcasts. WLAN radio and interface 876 and antenna 877 provide wireless connectivity when in a hot spot or within the range of an ad hoc, infrastructure or mesh based wireless LAN network. A Bluetooth EDR radio and interface 873 and antenna 875 provide Bluetooth wireless connectivity when within the range of a Bluetooth wireless network. Further, the communication device 870 may also comprise a WIMAX radio and interface 923 and antenna 925. SIM card 916 provides the interface to a user's SIM card for storing user data such as address book entries, etc. The communication device 870 also comprises an Ultra Wideband (UWB) radio and interface 883 and antenna 881. The UWB radio typically comprises an MBOA-UWB based radio.

Portable power is provided by the battery 924 coupled to battery management circuitry 922. External power is provided via USB power 918 or an AC/DC adapter 920 connected to the battery management circuitry which is operative to manage the charging and discharging of the battery 924.

Those skilled in the art to which the disclosure relates will appreciate that other and further additions, deletions, substitutions, and modifications may be made to the described example embodiments, without departing from the disclosure. 

1. A method of manufacturing a single-electron tunnel-junction device, comprising: providing a p-type substrate; disposing a pad oxide layer on the p-type substrate; disposing a nitride layer on the pad oxide layer; forming a nitride window in the nitride layer; disposing a field oxide in the nitride window; disposing a polysilicon gate over the field oxide; and diffusing an n-doped region in the p-type substrate, thereby forming at least one single-electron tunnel junction between the polysilicon gate and the n-doped region.
 2. The method as recited in claim 1 wherein a thickness of the pad oxide is approximately 1.2 nanometers.
 3. The method as recited in claim 1 wherein the field oxide is provided to a side of the p-type substrate.
 4. The method as recited in claim 1 wherein the n-doped region is diffused beneath the polysilicon gate to form a single tunnel junction.
 5. The method as recited in claim 1 wherein a first and second tunnel junction is formed at a first and second end, respectively, of the polysilicon gate.
 6. The method as recited in claim 1 further comprising providing a first mask for use with diffusing the n-doped region in the p-type substrate.
 7. The method as recited in claim 6 further comprising providing a second mask for use with disposing the polysilicon gate.
 8. The method as recited in claim 7 wherein a first and second single-electron tunnel junction are employed to help alleviate a mask-alignment mismatch between the first mask and the second mask.
 9. The method as recited in claim 1 further comprising: providing a mask for diffusing a plurality of n-doped regions defined by a first set of a plurality of active regions; providing a mask for disposing a plurality of polysilicon gates defined by a second set of a plurality of exposed regions, wherein an offset between a first member of the plurality of the exposed region of the first set differs in offset from a second member of the plurality of the exposed region of the second set; and fabricating a parallel redundant array of single-electron devices as a function of said offset.
 10. The method as recited in claim 9 wherein at least two single-electron devices of the parallel redundant array of single-electron devices have a differing capacitance from one another as a function of the offsetting of the at least two of the plurality of masks.
 11. A single-electron device, comprising: a p-type substrate; an n-doped region disposed in said p-type substrate; a pad oxide disposed over the n-doped region; a field oxide disposed to a side of the n-doped region; and a polysilicon gate disposed over the field oxide and also disposed over the pad oxide.
 12. The device as recited in claim 11 wherein the polysilicon gate, disposed over the pad oxide that is disposed over the n-doped region, forms a capacitance.
 13. The device as recited in claim 12 wherein the capacitance is substantially equal to a capacitance that is used to store a charge of only one electron.
 14. The device as recited in claim 11 further comprising: a second n-doped region disposed in said p-type substrate; and a second pad oxide disposed over the second n-doped region, the polysilicon gate being further disposed over the second pad oxide.
 15. The device as recited in claim 11 wherein a capacitance of the polysilicon gate disposed over the second pad oxide disposed over the second n-doped region compensates for a deficiency of a capacitance of the polysilicon gate disposed over the first pad oxide disposed over a first n-doped region.
 16. The device as recited in claim 11, wherein said single-electron device acts as a bias current reference.
 17. The device as recited in claim 11, wherein said polysilicon gate, disposed over the pad oxide that is disposed over the n-doped region, forms a tunneling junction.
 18. A parallel array of single-electron devices, comprising: a first single-electron device having: a p-type substrate, a first n-doped region disposed in the p-type substrate, a first pad oxide disposed over the first n-doped region, a field oxide disposed to a side of the n-doped region and a side of the p-type substrate, and a first polysilicon gate disposed over the field oxide and over the pad oxide; a second single-electron device having: a second n-doped region disposed in the p-type substrate, a second pad oxide disposed over the second n-doped region, a second polysilicon gate disposed over the field oxide and over said second pad oxide, at least two of said parallel single-electron tunnel devices of said redundant parallel having a differing capacitance as a function of a difference between: a first distance measured between the first n-doped region and the first polysilicon gate, and a second distance measured between the second n-doped region and the second polysilicon gate.
 19. The parallel array device as recited in claim 18 wherein a capacitance of at least one of the array of single-electron devices can store only a single electron.
 20. The parallel array device as recited in claim 18, further comprising a multiplexer coupled to a plurality of single-electron devices of said parallel array.
 21. The parallel array device as recited in claim 20, wherein said multiplexer selects at least one of the plurality of the single-electron devices that has an acceptable single-electron effect.
 22. The parallel array device as recited in claim 21, wherein a selected single-electron device acts as a bias current reference.
 23. The parallel array device as recited in claim 21, wherein said acceptable single electron effect is a voltage change of 0.1 Volts associated with said single-electron device. 